Flasks come in a number of shapes and a wide range of sizes. In some cases, flasks include a wider vessel “body” and one (or sometimes more) narrower tubular sections at the top called necks which have an opening at the top. Laboratory flask sizes are typically specified by the volume they can hold, typically in metric units such as milliliters (mL or ml) or liters (L or l). Laboratory flasks have traditionally been made of glass, but can also be made of plastic.
Flasks can be used for making solutions or for holding, containing, collecting, or sometimes volumetrically measuring chemicals, samples, solutions, etc. for chemical reactions or other processes such as mixing, heating, cooling, dissolving, precipitation, boiling (as in distillation), or analysis.